The invention relates to an apparatus for the injection moulding of synthetic products, comprising a die provided with a plurality of cavities, a discharge device and a robot device for receiving the products moulded in the cavities of the die and transferring those products to the discharge device.
Such an injection moulding apparatus is for instance disclosed in European patent application 0283644. The known apparatus is a machine for producing so-called "preforms" for synthetic containers such as PET (polyethylene terephthalate) bottles. The known apparatus has a die comprising a first die half, provided with a plurality of cavities, and a second die half, provided with the same number of cores. In the closed position of the die, the cores extend into the cavities, a space being present around each core in the cavity, which space is to be filled with synthetic material. After the synthetic material has been supplied in fluid form to the cavities and the synthetic material has cooled off sufficiently, the die is opened and a receiving plate of a robot device is brought before the product-carrying member of the die. In the apparatus described in European patent application 0283644, the preforms, after the die has been opened, are located on the cores, but it is also possible that, after the die has been opened, the preforms are located in the cavities. In the first case, the receiving plate of the robot device has cavities adapted to receive the products from the cores. In the second case, the receiving plate of the robot device has Dins or the like adapted to receive the products from the cavities. For this purpose, the die may be provided with ejecting means. Alternatively, the receiving plate may be provided with suction means for promoting taking of the products, optionally in combination with ejecting means of the die.
It is important that after the die has been filled up, the moulded products are removed from the die again as quickly as possible so as to obtain a shortest possible cycle period. This means that the products are still very warm and hence soft and vulnerable at the moment when the products are taken away by the receiving plate of the robot device. As the robot device should be ready again to take over the next set of preforms at the end of the next injection moulding cycle, this also means that the preforms can stay in the robot device only briefly and that the preforms are still very warm and vulnerable at the moment when the robot device delivers the preforms again to the discharge device. Typically, the discharge device comprises a conveyor belt and during the stay on the conveyor belt the preforms are cooled by air and/or fluid.
Because in this manner, the preforms are transferred twice before complete cooling and hardening has taken place, the chance of damage is relatively substantial. In the past, it was attempted to reduce the chance of damage by providing the receiving plate of the robot device with cooling means, such as cooling channels through which cooling fluid flows. However, in the case of a short cycle period, such a cooled receiving plate does not yet provide an optimum result.
For this reason, in European patent application 0283644 it is proposed that the receiving plate be provided with a number of receiving means for moulded products that is a multiple of the number of cavities of the die. In this manner, the moulded products, such as preforms, can stay in the cooled carrier plate for more than one cycle period and be cooled relatively long before the products are transferred to the discharge device.
A drawback of this known apparatus is that the receiving plate becomes large and heavy. Because the carrier plate should be moved back again between the die halves at the end of each injection moulding cycle, a quick reciprocating movement is necessary., which requires more energy as the mass of the receiving plate increases and which is moreover slowed down abruptly each time. Moreover, this quick reciprocating movement, stopping abruptly each time at the end of the path to be traversed by the receiving plate, increases the chance of damage to the products which are still located in the receiving plate.